Objectives: The aim of this study was to describe and highlight the characteristics of NS in order to compile a preliminary checklist for accurate diagnosis and intervention.

Method: An explorative, applied mixed method, multiple case study research design was followed. Purposive sampling was used to select four participants. A comprehensive assessment battery was compiled for data collection.

Results: The results revealed a distinct pattern of core stuttering behaviours in NS, although discrepancies existed regarding stuttering severity and frequency. It was also found that DS and NS can co-occur. The case history and the core stuttering pattern are important considerations during differential diagnosis, as these are the only consistent characteristics in people with NS.

Conclusion: It is unlikely that all the symptoms of NS are present in an individual. The researchers scrutinised the findings of this study and the findings of previous literature to compile a potentially workable checklist.

A therapy plan ideally reflects a thorough evaluation of all possible symptoms and etiologies. A checklist providing the distinctive features of NS will guide therapists to make a differential diagnosis between NS, developmental stuttering (DS), and acquired psychogenic stuttering (De Nil, 1999). A differential diagnosis remains challenging as similar symptoms may manifest, especially in the case of NS and psychogenic stuttering. A client with NS is often not aware of the dysfluencies but can be annoyed with his or her speech; similarly, in the case of psychogenic stuttering the client may be indifferent to his or her speech (Guitar, 2014). In both NS and psychogenic stuttering onset is sudden and dysfluencies are fairly consistent (Guitar, 2014).

Any form of stuttering and especially neurogenic stuttering (NS) can be viewed as a multidimensional speech disorder since it has an impact on the individual’s physical ability, emotions and mental health, environment, and psycho-social functioning (Yaruss, 2007). NS is classified as an acquired speech disorder (Theys et al., 2008). This form of stuttering is the most frequently occurring acquired form in both adults and children (Van Borsel & Tallieu, 2001). It is most often the result of a neurological incident, be it a stroke, a traumatic brain injury (TBI) or any other event that could damage brain functionality (Theys et al., 2008). For this reason it is imperative to manage NS according to the International Classification of Function (ICF). According to the model, the following need to be addressed: (1) impairments, which are the characteristics that can be observed; (2) disability, which refers to the speaker’s functional communication difficulties, and (3) the handicap, which refers to the negative influence on the speaker’s quality of life (Yaruss & Quesal, 2004).

Like any other form of stuttering, NS causes serious communication difficulties, possibly resulting in a perceived disability (Helm-Estabrooks, 1999). Communication difficulties can include social ineptitude and a negative self-perception as well as a negative perception of communication, which leads to social isolation, thus having a negative impact on the quality of life. Accurate and expeditious identification of NS can reduce or even prevent such communication difficulties (Manning, 2010). Currently the field of NS does not seem to be receiving much academic and clinical attention; but those professionals who have recognised this condition deem it crucial that SLPs are made aware of the characteristic features (Manning, 2010; Tani & Sakai, 2011; Theys et al., 2008; Shipiro, 2011).

In many cases, the reason why NS is not identified or diagnosed is that the individual displays no serious symptoms. It is also difficult to associate stuttering with fleeting neurological incidents that were not perceived as critical (Manning, 2010). These clients are often not even hospitalised, so no record of a TBI presents on their medical history. The clients with more severe TBIs are admitted to hospital with survival as the main goal and no attention can be given to speech evaluations at that time. These clients are then discharged without any warning of possible communication difficulties, such as NS, that can arise. The diagnosis can be further complicated when the onset of the NS occurs only months after the TBI.

Canter (1971) compiled a set of seven characteristics for the purpose of facilitating the accurate identification of persons with NS. Helm-Estabrooks (1999) adapted these characteristics to formulate six common symptoms. The symptoms Helm-Estabrooks (1999) identified are as follows:

1. Dysfluencies, which are equally observed on function words and content words during an utterance.
2. The speakers do not seem to be fearful or aware of the stuttering events. They do seem annoyed and surprised, however, at the occurrence of these events.
3. Repetitions, blocks and prolongations appear in all positions in words and expressions.
4. During stuttering events, people do not present with the secondary behavioural symptoms, such as facial contortions, eye blinking or fist clenching associated with the moment of stuttering.
5. The clients do not demonstrate adaptation effects.
6. Stuttering occurs consistently across different speech tasks and communication contexts.

Furthermore, Tani and Sakai (2011) cautioned therapists to take cognisance of the fact that some clients manifest added symptoms of aphasia and dysarthria.

More recently Lundgren, Helm-Estabrooks and Klein (2010) argued that the six symptoms as presented by Helm-Estabrooks (1999) are of questionable reliability as indicators. They contend that a person should present with all six of the symptoms associated with NS as well as a history of a neurological incident in order to be diagnosed with NS. In a study conducted by Perino, Famularo and Tarroni (2000), on the other hand, the client did not present with all six of the symptoms mentioned. They found that NS could be diagnosed due to the presence of a neurological incident and only two of the six symptoms associated with NS (Perino et al., 2000). General consensus amongst researchers has not been achieved regarding the characteristic symptoms of NS and their frequency. The frequency and type of symptom are in turn dependent on the severity of the neurological incident and the site of the lesion.

These discrepancies in the literature serve to emphasise the thorough and meticulous evaluation required if clinicians are to identify and address the specific symptoms as presented in any individual client. It also becomes apparent that professionals require information and guidance regarding the frequency of symptoms associated with NS. A checklist of symptoms associated with NS would facilitate differential diagnosis, as it would enable the SLP to consider all possible symptoms and etiologies in order to identify the presence of NS effectively, as well as to differentiate between this particular kind of stuttering and other forms of dysfluency.

When a clinician plans to assess an individual who stutters, several assessment batteries are available but none that address the unique symptomatology of NS (Manning, 2010; Shipley & McAfee, 2009). Van Borsel and Taillieu (2001) examined the feasibility of performing a differential diagnosis by using only speech sample analysis. The diagnosis was based on the opinion of the various professionals involved. These researchers had access to the recordings only. No other information, for example a case history of the client, was provided. They concluded that it is not sufficient to rely only on the speech characteristics of a client in order to diagnose and treat NS correctly. The current study, therefore, incorporated a complete case history and analysis of not only the audio recording but also a video recording, which provided the opportunity to analyse all observable behaviour associated with NS.

Although research findings on NS have been reported, there are various limitations to these studies. Single case studies (e.g. Perino et al., 2000) cannot necessarily be generalised to a larger NS population (as explained by Ringo & Dietrich, 1995). The study conducted by Theys et al. (2008) incorporated a larger number of clients with NS, but must be at risk for personal bias and subjectivity since the participants themselves were not included in the study; they were described by the SLPs only in terms of their speech patterns and presenting symptoms.

The current study includes multiple participants; it takes the form of a multiple case study. By using a case study approach the researchers were able to gather ample information, including a detailed account of the assessment process (Theys et al., 2008). The researchers were also able to give a more comprehensive representation of the NS population with multiple participants. Theys et al. (2008) suggested that data should be gathered that are more reliable and representative of a group of NS clients with similar conditions of origin – in other words, as in the case of this study, TBI. The study in hand was designed to address the shortcomings of previous studies.

As a result of the controversies and limited clinical guidelines in the literature, the following research question is posed: What are the distinctive characteristics of NS to be included in a preliminary differential diagnostic checklist?

All four participants had made minimal progress during previous stuttering therapy and had experienced frequent relapses. People who present with NS do not show the expected progress when traditional stuttering therapy techniques are used (Balasubramanian, et al. 2010; Lundgren et al., 2010). Only adults were included in the study as they are more likely to give a detailed account of their late childhood and early adulthood experiences relating to stuttering. The participants granted the researchers permission to contact their parents and/or relevant medical practitioners in order to obtain information regarding the participants’ medical history and early childhood. In the case of recent neurological incidents reports were obtained from the neurologist and general practitioners. The participants had to be proficient in either Afrikaans or English as these are the languages in which the researchers can converse with professional confidence. In order to be included in the study, the participants were required to have a history of a TBI incident. There is a correlation between NS and a TBI (Jokel, De Nil & Sharpe, 2007). Individuals who had suffered a stroke or have a neurological degenerative disorder were not included in the study, because research in a single etiology of NS is required (Theys et al., 2008). All four participants (see Table 1) were diagnosed with NS; however, one participant had a history of DS (normal dysfluency) as a pre-schooler. Gender was not a criterion for participant selection.

The constituent components of the comprehensive stuttering assessment were carefully selected to elicit all possible response types in order to formulate a comprehensive representation of each participant’s stuttering behaviour. This comprehensive representation was obtained by taking into account cognitive, affective, linguistic, motor and social functioning (Yaruss, 2007). In the case of this research study only high-functioning participants were included, and therefore the cognitive component was not evaluated formally. An information-gathering interview (Shipley & McAfee, 2009) was conducted as part of the selection process to confirm level of cognition. Cognitive awareness, however, was established utilising the same materials as with the affective and social component. The ability to have insight into one’s emotional responses and experience of stuttering was evaluated with: Overall Assessment of the Speaker’s Experience of Stuttering, or OASES (Yaruss & Quesal, 2010), Perceptions of Stuttering Inventory, or PSI (Woolf, 1967 as cited in Guitar, 2014), Perceptions of Self Semantic Differential Task (Kalinowski, Lerman & Watt, 1987) and Locus of control of behaviour scale, or LCB Scale (Craig, Franklin & Andrews, 1984 cited in Guitar, 2014). In addition to the Pragmatic Protocol (Prutting & Kirchner, 1987), an informal verbal and written assessment was conducted as a means of assessing the linguistic component. The speech-motor component was evaluated informally. Reading passages, stimulability probes and fluency-enhancing techniques were used to determine consistency or adaptation of dysfluency in speech. Spontaneous speech samples were collected to determine the severity and frequency of the stuttering behaviour. The instruments used to determine the abovementioned were: Stuttering Severity Instrument, or SSI (Riley, 1980), Fluency Charting Grid, Calculating the Dysfluency Index, Assessment of Associated Motor Behaviours, and Assessment of Physiological Factors Associated with Stuttering (Shipley & McAfee, 2009).

Spontaneous conversations in three different communication contexts provided the researchers with the opportunity to observe each participant’s communication abilities and consistency of stuttering behaviours when presented with different communication situations. An overall language assessment was deemed necessary so as to exclude the presence of a linguistic deficit. Language could not be assessed by means of formal standardised tests, as no uniform, culturally appropriate tests are available in South Africa to assess these abilities in each participant’s first language. However, by means of informal verbal and written assessment in the participants’ academic and/or business language (Afrikaans or English) the researchers were able to confirm the absence of any language deficits. An assessment of narrative writing was conducted to evaluate vocabulary, punctuation, spelling and story composition (Shipley & McAfee, 2009).

The study made use of inter-rater reliability since three independent interpretations of the video recordings were made by the researchers. The reliability of these interpretations was deemed high as the independent interpretations clearly correlated with one another. During the study, the researchers ensured internal validity by means of methodological triangulation by combining components of both qualitative and quantitative research (De Vos, 2002). The instruments that were used during each participant’s stuttering or dysfluency assessment are standardised and are specifically compiled to assess different stuttering behaviours, therefore enhancing the content validity of the study (Delport, 2002). Internal validity was further enhanced by making use of the purposive sampling method through which participants were selected on the basis of specific characteristics (Maxwell & Satake, 2006). By following this procedure, the researchers ensured that the most relevant data could be gathered.

The video and audio recordings enabled the researchers to analyse not only the speech and language components of the assessment but also the behavioural aspects such as the associated motor behaviours, core stuttering behaviours and secondary behaviours associated with stuttering.

The researchers viewed each participant’s video recording of the stuttering assessment. The data was then organised in file folders, from where it was converted to text units as a means of simplifying analysis. After rereading the researchers to familiarise themselves with the data set by rereading the data, the spiral circled to the category formation phase. The researchers noted regularities in the subsections of the assessment conducted on participants, which led to generating categories of meaning in which internal convergence and external divergence was established. These categories or patterns were then challenged in order to search for plausible explanations. The final phase consisted of the representation and visualisation of the characteristics of NS presented in a preliminary differential diagnostic checklist.

The quantitative data was analysed by using descriptive statistics such as simple frequency distribution. Triangulation of method was utilised by mixing quantitative and qualitative approaches in order to determine an overlap between the data (quantitative and qualitative) and consequently obtain more comprehensive results.

With regard to family history, the findings of this study concur with reports by Manning (2010) and Yairi (2007) that individuals with a family history of DS are predisposed for the occurrence of NS. Ludlow and Loucks (2003) provide an additional affirmation of the DS–NS connection, namely: the presence of DS results in increased susceptibility to NS following a neurological incident.

All the participants in this study presented with a history of a closed TBI which resulted in diffuse brain damage. P1, P2 and P4 presented with appropriate cognitive awareness. It can therefore be deduced that cognitive awareness is not always negatively affected in all cases of NS in the presence of a history of a TBI.

Results on pragmatic behaviour were obtained by means of the Pragmatic Protocol (Prutting & Kirchner, 1987). All four participants presented with pragmatic deficits associated with a neurological incident. Pragmatic behaviours characteristic of DS were also observed in P4. Depending on the nature of the neurological incident, additional pragmatic deficits may be present (Dardier et al., 2011; Douglas, 2010). During differential diagnosis it is important to identify the pragmatic deficits related to the neurological incident, as well as pragmatic deficits associated with the stuttering behaviour. Pragmatic behaviours that were observed (P1–P4) to be associated with the NS included deficits in cohesion, physical proximity, topic initiation and maintenance, and conciseness. These behaviours are consistent with pragmatic breakdown found in persons with left and right hemisphere brain damage (Bloom & Obler, 1998). Pragmatic behaviours associated with DS (P4) included deficits in turn-taking ability and paralinguistic aspects in an attempt to disguise or avoid the stuttering behaviour (Guitar, 2014). Therefore, it is of importance to be vigilant in the identification of specific pragmatic deficits associated with a neurological incident. The nature of the different pragmatic deficits can guide the SLP in terms of differential diagnosis.

On assessing adaptation and consistency of stuttering behaviour, it was noted that consistency was high and adaptability low. This is characteristic of NS (Manning, 2010) and is an important characteristic to identify during the differential diagnosis between NS and DS. By means of fluency probes P2 was able to maintain fluency for a short period of time. The other three participants achieved fluency during automatic speech tasks, but were not able to produce more fluent speech when presented with the different fluency probes. It can be deduced that some persons presenting with NS do benefit from fluency probes, but the application is limited in the sense that communication presents as deviant from what is deemed natural speech. Three out of the four participants who were included in the study did not benefit from the various stimulability probes. Balasubramanian et al. (2010) and Helm-Estabrooks (1999) reported similar findings. Consequently, poor adaptation of speech when the PWS is presented with fluency probes should be considered an indicator in the differential diagnosis between NS and DS.

In general, NS poses challenges with regard to differential diagnosis. Diagnosis of NS is complicated by the long-term nature of the problem, co-occurring language disorders and the additional presence of DS. The percentage of core stuttering behaviour relative to total occurrence of all behaviours across participants is presented in Figure 1.

FIGURE 1: Predominant core stuttering behaviours presented by P1 – P4.

Figure 1 clearly illustrates that the participants presented an array of core stuttering behaviours that exemplify the distinctive features of NS. Repetitions were the most dominant core stuttering behaviour which was present in all four participants. Repetitions consisted predominantly of sound and part-word repetitions in the initial, medial and final position of words. The presence of sound and part-word repetitions in the medial and final position of words is characteristic of NS, as described by Helm-Estabrooks (1999) and Tani and Sakai (2011). Furthermore, the findings of initial sound and part-word repetitions concur with the findings in the study conducted by Tani and Sakai (2011). Although part-word repetitions are generally accepted as core stuttering behaviours present in NS, these may also occur in DS and PS. For this reason a holistic approach is essential in order to identify other co-occurring characteristics predicting neurogenic involvement.

Associated motor behaviours in an attempt to escape the stuttering moments were present in three of the participants (P1, P3 and P4). In addition, in the case of P2 apraxia-like symptoms, such as oral searching and groping movements, were observed. This corroborates with findings by Tani and Sakai (2011), suggesting that the SLP should be aware of soft neurological signs during the differential diagnosis between DS an NS.

The case history and the core stuttering patterns are an important consideration during differential diagnosis of NS. The occurrence of a neurological incident and the core stuttering patterns are the only consistent characteristics in individuals presenting with NS and they should be considered predictors of this dysfluency disorder. Other factors that may be considered during differential diagnosis are variable, but it is important to note that the presence of one NS symptom in combination with the detailed case history guides the differential diagnosis and planning of NS intervention (Helm-Estabrooks, 1999). This study found that it is unlikely that all the symptoms of NS will be present in a single client. This finding concurs with the study conducted by Perino et al. (2000).

Additional findings of this study were similar to those reported in recent literature regarding the occurrence of NS in combination with DS (Manning, 2010; Yairi, 2007). It is evident that there is much yet to be discovered about the complexity of NS. It was found that DS can present simultaneously with NS, and that the onset of NS can occur in early childhood. This finding highlights the importance of making a clear differential diagnosis in early childhood in order to ensure the most effective intervention from an early age.

The Preliminary Checklist for Differential Diagnosis of Neurogenic Stuttering (see Appendix 1) takes into consideration all the relevant characteristics for differential diagnosis of NS. Besides the findings reported in current literature, additional features were identified in this study, for instance some participants presented with increased cognitive awareness, contradicting findings by Helm-Estabrooks (1999) and Guitar (2014). The characteristics identified in the participants as well as the features described in the current literature were included in the compilation of the preliminary checklist. These characteristics are categorised as either predictive or non-predictive factors. A high occurrence of predictive factors is indicative of NS, whereas non-predictive factors may be present in either NS, DS or psychogenic stuttering. The checklist has been compiled in such a manner that it should be user friendly as the SLP needs to answer only ‘yes’ or ‘no’ questions. Furthermore, guidelines for the interpretation of responses are included in the checklist. The applicability of the compiled checklist was evaluated informally by a professional speech-language pathologist with extensive experience in working with PWS. The checklist was deemed comprehensive and potentially a valuable tool.

Since the differential diagnostic applicability of this tool has not been researched in depth, the checklist should be evaluated in future research. It is recommended that the checklist should be implemented on a diverse group of individuals presenting with fluency disorders. In addition to the application of the preliminary checklist on a diverse group, an increase in the sample size is recommended for future research. This is considered necessary since the nature of this study’s explorative research design led to the inclusion of a small sample size. Although the preliminary checklist appears to be comprehensive, further research is warranted in order to determine the validity and reliability of the tool. In addition, future research is needed to determine the relationship between DS and the long-term nature of NS with regard to the level of awareness of the stuttering behaviours as well as the specific effects on overall communication.

Bless, C., & Higson-Smith, C. (2000). Fundamentals of social research methods: An African perspective (2nd edn., pp. 63–81). Cape Town: Juta.

Bloom, R.L., & Odler, L.K. (1998). Pragmatic breakdown in patients with left and right brain damage: Clinical implications. Journal of Neurolinguistics, 11, 11–20. http://dx.doi.org/10.1016/S0911-6044(98)00002-5

Canter, G.J. (1971). Observations on neurogenic stuttering: A contribution to differential diagnosis. British Journal of Disorders of Communication 6, 139–143. http://dx.doi.org/10.3109/13682827109011539

Craig, A., Franklin, J., & Andrews, G. (1984). A scale to measure locus of control of behaviour. British Journal of Medical Psychology, 57, 173–180. http://dx.doi.org/10.1111/j.2044-8341.1984.tb01597.x

Creswell, J.W. (1994). Research design: Qualitative and quantitative approaches. Thousand Oakes, CA: Sage.

Dardier, V., Bernicot, J., Delanoë, A., Vanberten, N., Fayada, C., Chevignard, M. et al. (2011). Severe traumatic brain injury, frontal lesions, and social aspects of language use: A study of French-speaking adults. Journal of Communication Disorders, 44, 359–378. http://dx.doi.org/10.1016/j.jcomdis.2011.02.001

Delport, C.S.L (2002). Quantitative data collection methods. In A.S. de Vos (Ed.), Research at grass roots. A primer for the caring professions (2nd edn., pp. 165–196). Pretoria: Van Schaik Publishers.

De Nil, L.F. (1999). Stuttering: A neurophysiological perspective. In N.B. Ratner, & E.C. Healey (Eds.), Stuttering research and practice: Bridging the gap (pp. 85–102). Mahwah, NJ: Lawrence Erlbaum Associates, Inc., Publishers.

De Vos, A.S. (2002). Combined quantitative and qualitative approach. In A.S. de Vos (Ed.), Research at grass roots. A primer for the caring professions (2nd edn., pp. 363–371). Pretoria: Van Schaik Publishers.

De Vos, A.S. (2002). Qualitative data analysis and interpretation. In A.S. de Vos (ed.), Research at grass roots. For the social sciences and human service professions (2nd edn., pp. 339–354). Pretoria: Van Schaik Publishers.

Douglas, J.M. (2010). Relation of executive functioning to pragmatic outcome following severe TBI. Journal of Speech, Language and Hearing Research, 53, 365–382. http://dx.doi.org/10.1044/1092-4388(2009/08-0205

Gazzolo, D., Grutzfeld, D., Michetti, F., Toesca, A., Lituania, M., Bruchettini, M. et al. (2004). Increased S100B in cerebrospinal fluid of infants with bacterial meningitis: Relationship to brain damage and routine cerebrospinal fluid findings. Clinical Chemistry, 50, 941–944. http://dx.doi.org/10.1373/clinchem.2003.021048

Guitar, B. (2014). Stuttering an integrated approach to its nature and treatment. (4th edn.). Baltimore, MD: Lippincott, Williams & Wilkins.

Helm-Estabrooks, N.A. (1999). Stuttering associated with acquired neurologic disorders. In R.F. Curlee (Ed.), Stuttering and related disorders of fluency (2nd edn., pp. 255–268). New York, NY: Thieme Medical Publishers.

Jokel, R., De Nil, L., & Sharpe, K. (2007). Speech disfluencies in adults with neurogenic stuttering associated with stroke and traumatic brain injury (case study). Journal of Medical Speech-Language Pathology, 15(3), 243–270.

Kalinowski, L.S., Lerman, J.W., & Watt, J. (1987). A preliminary examination of self and others in stutterers and non-stutterers. Journal of Fluency Disorders, 12, 317–331. http://dx.doi.org/10.1016/0094-730X(87)90030-1

Leedy, P.D. & Ormrod, J.E. (2014). Qualitative research. In P.D. Leedy & J.E. Ormrod (Eds.), Practical research: Planning and design (10th edn., pp. 141–172). Essex: Pearson Education Limited.

Ludlow, C.L., & Loucks, T. (2003). Stuttering: A dynamic motor control disorder. Journal of Fluency Disorders, 28, 273–295. http://dx.doi.org/10.1016/j.jfludis.2003.07.001

Lundgren, K., Helm-Estabrooks, N., & Klein, R. (2010). Stuttering following acquired brain damage: A review of literature. Journal of Neurolinguistics 23, 447–454. http://dx.doi.org/10.1016/j.jneuroling.2009.08.008

Manning, W.H. (2010). Clinical decision making in fluency disorders. (3rd edn.). Clifton Park, NY: Delmar Cengage Learning.

Maxwell, D.L., & Satake, E. (2006). Research and statistical methods in communication sciences and disorders. New York, NY: Thomson Delmar Learning.

Perino, M., Famularo, G., & Tarroni, P. (2000). Acquired transient stuttering during a migraine attack. Headache 40, 170–172. http://dx.doi.org/10.1046/j.1526-4610.2000.00025.x

Pienaar, P. de V., & Hooper, A.G. (1968). In die wildtuin [In the game reserve]. In ’n Afrikaanse fonetiese leesboek [An Afrikaans phonetic reader]. Pretoria: Van Schaik Publishers.

Prutting, C.A., & Kirchner, D.M. (1987). A clinical appraisal of pragmatic aspects of language, Journal of Speech and Hearing Disorders, 52(2), 105–119.

Riley, G.D. (1980). Stuttering severity instrument Tigard, OR: C.C. Publications, Inc.

Ringo, C., & Dietrich, S. (1995). Neurogenic stuttering: An analysis and critique. Journal of Medical Speech-Language Pathology, 3(2), 111–122.

Shipley, K.G., & McAfee, J.G. (2009). Assessment in speech–language pathology. A resource manual. (4th edn.). Clifton Park, NY: Delmar Cengage Learning.

Shapiro, D.H. (2011). Stuttering intervention. A collaborative journey to fluency freedom. (2nd edn.). Austin, TX: PRO-ED, Inc.

Di Sciullo, A.M., Piattelli-Palmarini, M., Wexler, K., Berwick, R.C., Boeckx,C., Jenkins, L., et al. (2010). The biological nature of human language. Biolinguistics, 4, 4–34. http://www.biolinguistics.eu

Tani, T., & Sakai, Y. (2011). Analysis of five cases with neurogenic stuttering following brain injury in the basal ganglia. Journal of Fluency Disorders, 36, 1–16. http://dx.doi.org/10.1016/j.jfludis.2010.12.002

Theys, C., Van Wieringen, A., & De Nil, L.F. (2008). A clinician survey of speech and non-speech characteristics of neurogenic stuttering. Journal of Fluency Disorders, 33, 1–23. http://dx.doi.org/10.1016/j.jfludis.2007.09.001

Van Borsel, J., & Taillieu, C. (2001). Neurogenic versus developmental stuttering: An observer judgement study. Journal of Communication Disorders, 34, 385–395. http://dx.doi.org/10.1016/S0021-9924(01)00057-0

Woolf, G. 1967. Perceptions of stuttering inventory (PSI). British Journal of Communication Disorders 2, 158–177. http://dx.doi.org/10.3109/13682826709031315

Yairi, E. (2007). Subtyping stuttering I: A review. Journal of Fluency Disorders, 32, 165–196. http://dx.doi.org/10.1016/j.jfludis.2007.04.001

Yaruss, J.S. (2007). Application of the ICF in fluency disorders. Seminars in Speech and Language, 28(4), 312–322. http://dx.doi.org/10.1055/s-2007-986528

Yaruss, J.S., & Quesal, R.W. (2004). Stuttering and the International Classification of Functioning, Disability and Health (ICF): An update. Journal of Communication Disorders, 37, 35–52. http://dx.doi.org/10.1016/S0021-9924(03)00052-2

Yaruss, J.S., & Quesal, R.W. (2010). OASES: Overall assessment of the speaker’s experience of stuttering. Bloomington, MN: Pearson/AGS.